1. Origin of the Invention
The invention described herein was made in the performance of work under a NASA contract, and is subject to the provisions of Public Law 96-517 (35 USC 202) in which the Contractor has elected not to retain title.
2. Technical Field
The invention is related to virtual reality systems and in particular to the type of virtual reality systems proposed for use in flight simulation and pilot training devices. More specifically, the invention is a flight control system for virtual navigation in inertial space having no ground plane or preferred orientation.
3. Background Art
Virtual reality displays have become practical with the combination of computers and video image processors. Computer-controlled video imaging has led to computerized simulation of images, which in turn has led to simulation of images responsive to user-controlled interactions. In particular, Foley, "Interfaces for Advanced Computing," Scientific American, October, 1987, pages 127-134, discloses, for example, the use of a wired glove worn by the computer user and connected to a computer that generates images on a monitor responsive to movements of the glove to give the user the sensation of handling objects, a virtual reality. Fisher et al., "Virtual Environment Display System," ACM 1986 Workshop on Interactive 3D Displays, Oct. 23-24, 1986, Chapel Hill, N.C., discloses head-mounted stereoscopic displays controlled by the users movements, such as might be useful in practicing movements required to perform certain tasks. Such virtual reality systems, which typically require supercomputers, were foreshadowed by flight simulators for pilot training, which used ordinary computers to control the image display. Head-mounted, position sensitive displays were shown by D. Engelbart as early as 1962.
Flight simulators of the type employed in aircraft pilot training provide a frame of reference in the image presented to a trainee, dominated by a ground plane, giving the pilot a constant horizontal reference. The flight simulator alters the scene observed by the trainee in accordance with flight control commands from a joy stick controlled by the trainee. This joystick serves the same function in flight simulation as the glove serves in the virtual reality system of the publication by Foley referenced above. The image processing is limited in that the flight movements are treatable as perturbations from horizontal flight.
In one type disclosed in U.S. Pat. No. 5,137,450, a number of video projectors project different perspective views of a scene to different "windows" surrounding the trainee's field of view. In another type disclosed in U.S. Pat. Nos. 5,134,521; 4,985,762; 4,310,849 and 4,348,185, the display is a device very close to the trainee's eyes, facilitating a more realistic panoramic image. In such displays, the image follows the movements of the trainee's head to present a more realistic image.
Flight simulators employing computer-generated images have presented images of targets to be viewed by the trainee oriented in accordance with the pilot's head, as disclosed in U.S. Pat. No. 4,303,394.
Because of the relatively limited movements and rotations simulated by a flight simulator, it is possible to actually move the simulator to simulate many of the accelerations commanded by the trainee, as disclosed in U.S. Pat. No. 4,487,410. Since most accelerations correspond to perturbations from horizontal flight, simulating such accelerations is quite practical. This is comparable in the entertainment field to the Disney-Lucas "Star-Tours" ride at Disneyland.
A corollary of the foregoing is that known flight simulators are not particularly useful for simulating flight beyond earth's atmosphere, and particularly flight through inertial space where there is no preferred "horizontal" direction or horizon. Since there is no particular earth or planetary coordinate system in flight through inertial space by which to define "horizontal", such flight cannot be treated as mere perturbations from a preferred "horizontal" orientation. This is because an entire flight in inertial space might be straight "down" or straight "up" or in an "upside down" orientation with many rotations through 360 degrees, any of which would be beyond the capabilities of a flight simulator. Moreover, if a standard flight simulator were modified for use in simulating flight through inertial space by removing the ground plane or horizon from the simulated image, the trainee would have no reference in the image from which he could reliably discern his orientation and rotations.
This is in fact a fundamental problem in any flight through inertial space, simulated or real: giving the pilot a quick and accurate reference to sense orientation. However, there is no technique known that addresses this problem. For example, U.S. Pat. No. 4,984,179 discloses a computer-generated three-dimensional display that permits the viewer to command rotations about any axis and to view the results in this display, but is not capable of simulating translational movement along more than one axis. Moreover, since this technique implicitly assumes a ground plane or horizon, no provision is made for solving the problem of maintaining in the displayed image a reference of the trainee's orientation in three dimensions.
Suppose a person, the traveller, is immersed in a virtual reality. The virtual reality is made of graphic images synthesized by computer from real or model data and projected into the traveller's eyes by means of binocular, full field-of-view display screens, such as the EyePhones.TM. of VPL, Inc. Let us call these, generically, virtual reality displays (VRDs). Naturally, the images may be accompanied by synthesized audio and other media to further enhance the illusion of reality, but the subject here is the images. The projection parameters that determine the apparent parallax, point of view, and gazing direction of the traveller are determined by the virtual reality control system (VRCS). Most proposed or existing VRCS's involve devices that sense the position and orientation of the traveller's head and adjust the projection parameters to maintain the illusion that the traveller is immersed in a real scene. When the traveller turns his head, a new gazing direction is calculated from the new head orientation sensed by the VRCS. Usually, the computed gazing direction is the same that would obtain in a real reality. This maximally real gazing direction most maintains the illusion of reality. Likewise, when the traveller moves around within the sensing range of the VRCS, a new point of view is calculated from the sensed position. Many interesting mappings from the position and orientation sensed by the VRCS to the projection parameters can be used to create a variety of illusions, and such mappings are a fertile ground for experimentation and invention. The subject, here, however, is the sensing of the position and orientation. Let us assume the most straightforward mappings for the time being. The VRCS must repeatedly sense position and orientation, and the rest of the virtual reality system must quickly calculate a new point of view and gazing direction. This must be done quickly enough that the viewer cannot perceive any delay between the instant of movement to a new position and orientation and the instant of display of a new projection using the new point of view and gazing direction, that is, within the persistence threshold of the human visual system. Typically, so long as the delay is less than about 1/30 seconds, the illusion of reality is maintained. The head-sensing control metaphor is adequate for some two-dimensional virtual realities, say walking around a virtual office or moving within a virtual tennis court, but is not adequate, alone, for three-dimensional realities. How is one to fly a virtual airplane, for example, by head movements alone? In the case of airplanes, providing the traveller with a joystick, rudder pedals, and a throttle is probably the best thing to do. Travellers who know how to fly real airplanes will find these controls immediately useful in virtual spaces, and travellers who do not know how to fly will learn something useful for the real world by using these controls. One might, on option, "fudge" the exact metaphor of flight to provide quick, non-physical position changes and play other useful games with the kinematics. However, the airplane metaphor presupposes a horizon or ground plane, so is not fully three-dimensional. Some other control metaphor is required for untethered, free flight in three-dimensional space.
Accordingly, it is an object of the invention to provide an apparatus for displaying to a pilot or trainee the image of a scene surrounding a vehicle traveling in inertial space in response to rotational and translational acceleration commands by the pilot in six degrees of freedom.
It is a further object of the invention to provide a flight control apparatus having six degrees of freedom of acceleration or velocity control by a pilot that displays to the pilot the image of a scene surrounding a vehicle or pod containing the pilot traveling through inertial space, the image itself including a superimposed figure providing the pilot an instant reference of orientation.
It is a related object of the invention to provide a flight control apparatus having six degrees of freedom of acceleration or velocity control by a pilot that displays to the pilot the image of a scene surrounding a vehicle or pod containing the pilot traveling through inertial space, the image itself including a superimposed set of geometric figures whose relative orientations provide the pilot an instantaneous reference of orientation with respect to some fixed coordinate system.
It is a still further object of the invention to provide a virtual reality display corresponding to a flight control apparatus having six degrees of freedom of acceleration or velocity control by a pilot that displays to the pilot the image of a scene surrounding a vehicle or pod containing the pilot traveling through inertial space, the image itself including a superimposed set of geometric figures whose relative orientations provide the pilot an instantaneous reference of orientation with respect to some fixed coordinate system.
It is a related object of the invention to provide such a set of geometric figures superimposed on the scene and apparently surrounding the pilot that include a first set of geometric figures whose orientations are fixed to the pilot's vehicle and a second set of geometric figures whose orientations are fixed with respect to a fixed global, interplanetary or interstellar coordinate system.
It is a yet further object of the invention to provide, in such a virtual reality display, the superimposed set of geometric figures which include a first set of orthogonal great circles about the three orthogonal axes of the flight vehicle or pod and centered at and surrounding the pilot's head and a second set of orthogonal great circles about the three orthogonal axes of a fixed or interstellar coordinate system, also centered at and surrounding the pilot's head.
It is a still further object of the invention to provide, in such a display, tick-markings or off-axis secondary circles at periodic arc lengths along each of the main circles that permit the pilot to instantly gauge approximate angles of rotation about any axis.
It is yet another object of the invention to permit a pilot in such a virtual reality display to instantly scan among a set of velocities for easy navigation in simulated flight.